"It was difficult for me to accept the fact, as much as she was psychotic, that it was a pure mental disorder," said Dr. Najjar.

STATEN ISLAND, N.Y., - Susannah Cahalan has no memory of the day Dr. Souhel Najjar walked into her room at NYU-Langone Medical Center for the first time. She later learned that he sat at her bedside, held her hand and looked directly into her eyes as he promised to figure out what was wrong, something the other doctors no longer did.

Dr. Najjar filled pages of notes detailing Ms. Cahalan's symptoms as described by her family: Numbness on the left side of her body, mood swings at work, seizures and hallucinations of her father beating her stepmother, Civil War paintings coming to life and a statue of Buddha smiling at her when she locked herself in the bathroom.

He studied the results of highly-specialized, multi-million dollar medical tests and he reviewed past diagnoses ranging from mononucleosis to alcohol withdrawal to bipolar disorder to schizophrenia-related illnesses.

But Dr. Najjar -- often referred to as a gentle version of television's Dr. House for his ability to unlock the most complex of medical mysteries -- wasn't buying any of it in a 24-year-old with no previous or family medical history.

"It was difficult for me to accept the fact, as much as she was psychotic, that it was a pure mental disorder," said Dr. Najjar, an associate professor of neurology at NYU-Langone and also the director of neuroscience at Staten Island University Hospital. 

The first clue was her first symptom: Numbness on the left side.

"I realized that's when her disease started before she became psychotic," said Dr. Najjar. 

NEEDED PROOF 

"I needed to prove to many doctors involved in her care before me that this was actually a neurological disease. I had to find a test in my mind that proved it."

So he handed Ms. Cahalan a pencil and a piece of paper and asked her to draw a clock.

"When I looked at the drawing, I was completely taken back in that she squeezed all the numbers from one to 12 only on the right side of the clockface, and she left the left side of the clockface totally empty," Dr. Najjar said.

"She ignores, neglects, doesn't even see anything on the left side of the hemisphere, which is usually the function of the right side of the brain.

"Here's the evidence this started on the right side of the brain. It correlated with what her parents told me early on before she was sick or psychotic or she had seizures, she had numbness on the left side."

A brain biopsy confirmed Dr. Najjar's hunch: There was inflammation on the right side of Ms. Cahalan's brain.

He diagnosed her with autoimmune encephalitis, a rare, but easily treatable disorder, which can present with psychiatric symptoms.

Essentially, her body was attacking her brain -- or "setting her brain on fire." 

A STORY TO TELL 

Dr. Najjar's simple explanation of a complicated disorder became the basis of "Brain On Fire: My Month of Madness," a New York Times best-selling memoir written last year by Ms. Cahalan.

Her skills as a reporter for the New York Post helped her piece it all together: She interviewed Dr. Najjar, her family and friends, looked at her medical records and read a detailed diary kept by her father.

She decided to write the book after an article in the Post -- "My mysterious month of madness" -- brought an intense level of interest through e-mails and phone calls.

"I just knew I needed to do it on a larger level, to get the word out about the disease" said Ms. Cahalan, currently on a book tour for the paperback version. "I never thought anybody would read it."

Her initial symptoms manifested as her life picked up speed: She had just been hired full-time by the Post, she was in a new relationship and she was living in her first apartment.

"I didn't know what I was going to do day-to-day, which was exciting, but also made it harder to figure out there was something wrong with me," she said.

"I tried to make sense of it and thought maybe all these changes -- the new job, the new boyfriend, the new apartment -- were causing these feelings." 

INITIAL DEAD-ENDS 

It was the numbness that convinced her she needed to see a neurologist. But all the diagnostic tests were negative, except for slightly enlarged lymph nodes, thus the mono diagnosis.

She suffered her fist seizure while watching the PBS show, "Spain -- On the Road Again," with her boyfriend.

It was one of the last moments she remembered for a month.

Her parents, fearing for their daughter's safety, took her to NYU. She was rushed to the epilepsy unit when she had her third grand mal seizure while waiting in the emergency room.

In the hospital, Ms. Cahalan's behavior became more erratic and she slipped into a catatonic state.

Two weeks into her month-long stay, Dr. Najjar was brought in to consult.

She was released from the hospital soon after his diagnosis, returned to work seven months later and was treated with a course of steroids for a year.

"I can't really remember a time when I felt like myself again during the first year," she said. "It was in stages. I really just had these glimmers of memories."

Dr. Najjar downplays his role as hero in Ms. Cahalan's book. Instead, he thinks the book should become required reading for both veteran physicians and students in their first years of medical school.

"This taught me a lesson and should teach a lot of physicians a lesson," he said.

"When you go into a patient's room, and the patient is very psychotic, severely impaired, catatonic, not interacting, please, please give a chance to that patient and communicate with that patient, and do not consider him an object.

"After all, the patient has the clue for the disease and the diagnosis."